Thermoplastic elastomers have been prepared by connecting glassy segments with rubbery segments in the form of block or graft copolymers. Graft copolymers having the proper structure for good thermoplastic elastomer properties can be prepared according to cationic grafting "from" polymerization techniques.
While the cationic graft polymerization prior art specifically teaches the use of inert solvent, monomer and alkyl aluminum coinitiator, it teaches nothing about the need for, use or effect of water on both the grafting rate and ultimate monomer conversion. This same prior art also fails to teach or suggest anything about the use or effect water, as herein described and claimed, would have as regards the improved tensile and service temperature properties of my graft polymer. I have discovered that the addition of water increases both the rate of grafting and the ultimate monomer conversion. Thus the presence of a small amount of water in the polymerization medium is not only desirable, but necessary where high monomer conversions are required.